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    SubjectRe: Benefits from computing physical IDE disk geometry?
    Chuck Ebbert wrote:

    >>If RAID1 can use the generic elevator then it should. I
    >>guess it can't though.
    > No, but it is feeding IO requests into the elevators of the
    >block devices below it. For a given read, all it wants to do
    >is pick one device to handle the work. If it could look into
    >the queues maybe it could make better decisions.
    OK right. As far as I can see, the algorithm in the RAID1 code
    is used to select the best drive to read from? If that is the
    case then I don't think it could make better decisions given
    more knowledge. It really wants to know if the disk head is
    close to request x however it is impossible to tell where the
    disk head will be by the time request x is the next in line
    for that disk, regardless if it can look at the low level
    queues or not.

    It seems to me that a better way to layer it would be to have
    the complex (ie deadline/AS/CFQ/etc) scheduler handling all
    requests into the raid block device, then having a raid
    scheduler distributing to the disks, and having the disks
    run no scheduler (fifo).

    In practice the current scheme probably works OK, though I
    wouldn't know due to lack of resources here :P

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      Last update: 2005-03-22 13:34    [W:0.019 / U:40.100 seconds]
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